The issuer
USDT is worth a dollar because Tether says it will redeem it for one. If its reserves fell short, the price could drop below a dollar.
Tether has been fined over this before. In 2021 the CFTC ordered it to pay $41 million over claims that USDT was fully backed by US dollars, and the New York Attorney General settled with Tether and Bitfinex for $18.5 million. Neither admitted wrongdoing in the New York case.
Tether can also freeze USDT at an address. Its transparency page lists those tokens as quarantined: they stay where they are but cannot be sent. See Tether frozen USDT.

